Unity bringing Error!?

So I am using Unity 5.3.5f1 32-bit on Windows 10. I typed a script (see below) and unity is telling me I have an error at (19,1)! (Also see below)

Script:

using UnityEngine;
using System.Collections;

public class Planet1Orbit : MonoBehaviour {

	// Use this for initialization
	void Start () {
		float xvalue = 129.5f;
	}
	
	// Update is called once per frame
	void Update () {
		transform.position = new Vector3(xvalue, -17.8, 108.9);
		xvalue = xvalue - 0.5;
		if (xvalue == -32.5)
		{
			xvalue = 129.5f;
	}
}

Error:

Please reply Asap

This error is because of something called scope.

Scope means that is you declare a in your Start() function it will not apply to Update().

Fixed code:

 using UnityEngine;
 using System.Collections;
 
 public class Planet1Orbit : MonoBehaviour {

     float xvalue = 129.5f;

     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
     void Update () {
         transform.position = new Vector3(xvalue, -17.8, 108.9);
         xvalue = xvalue - 0.5;
         if (xvalue == -32.5)
         {
             xvalue = 129.5f;
     }
 }